Direct-view electrical storage tube and methods of operating same



yDIRECT-VIEW ELLECTRICAL STORAGE TUBE AND METHODS oF OPERATING SAMEFiled 'Aug. 14, 1953 'hihi-"15,1958 V H o HK Em. 2,843,799v

- pff/719701Z wr/0 INI/ENTORS United States DIRECT-VIEW ELECTRICALSTORAGE TUBE AND METHODS OF OPERATING SAME Harvey 0. Hook and Max Knoll,Princeton, N. J.,'as signers to Radio Corporation of America, acorporation of Delaware l Application August 14, 1953, Serial No.374,172 8 Claims. (Cl. 315-12) filed May 29, 1953, by Harvey O. Hook.

A number of presently known signal storage and display systems are usedin connection with radar Systems, ground-taair private linecommunication systems, and

the like. In order to obtainthe features of both signal storage andsignal display these storage and display 4systems generally require oneor more electrical storage tubes in combination with a separate displaytube. Such arrangements are complicated, relatively expensive, andoccupy excessive amounts of space which could be used to betteradvantage, particularly in airborne systems., It is highly desirable insuch instances to combine the features of storage and display in asingle tube. f

. Such a tube has been developed and is described in detail in patentapplication Serial No. 295,768, filed June 26, 1952, by Max Knoll. Insaid application data stored and displayed by the direct View tube iscompletelyv and almost instantaneously erased by manually adjustingpotentials applied to certain electrodes contained therein. Such anerasing technique may be satisfactory for erasing stored transients vandthe like. However, the erasure atent ice technique is disclosed whereina fractional portion of the total stored image pattern is erasedk duringeither the line or frame deflection flyback interval. Byv

f line of old data may be completely erased just prior to requirementsfor radar and various other systems arev 'Y more exacting.

In radar systems providing either rectilinear B-scanY or polarcoordinate P. P. I. .(plan-p'ositiondndication)' type presentations, itis undesirable to completely erase a storedframe of information beforecommencing to l write a new frame of data derived in a succeeding searchinterval. In most of such radar.r systems four to siX seconds isrequired for completely displaying data derived Iduring a'"360 azimuthsearch.y If there is instantaneous and complete erasure the four to sixsecond time interval must again transpire before the new frame ofinformation is completely displayed. A further disadvantagey of completeerasure atfthe Vendl of the writing of a given frame is that the eyedoes not integrate the data last l written and there is an apparentintensity variationor Moreover, information available during shadingeffect. y the erase period is not stored and therefore is lost.

In a more recently led patent application of Harold Borkan, Serial No.306,706, filed August 27, 1952, 'an erasing vtechnique is disclosed'forthe direct-view tube which 'is ,adaptedl for erasing Bscan or P. P. I.type displays. According to this technique the tube storage electrodeassembly includes a plurality of individually insulated charge storagesections. storage section automatically isl controlled for Verasure in'an vorderly sequence so that old data stored ona given storage sectionis erased substantially immediately before new data is to be writtenthereon.

In the application of Harvey Hook, cited above, Serial The potential ofeach N o. 4358,36l, filed May 29,` 1.953, a further erasingj beingreplaced with a line of new data. By performing erasing during the framedeection flyback time signal integration may be achieved.

An object of the present invention is to provide improved methods andmeans for storing and displaying signal intelligence.

Another object of the invention is to provide improved methods and meansfor utilizing a direct-view storage tube. Y

Another Object of the invention is to provide improved methods and meansfor either erasing or holding data stored and displayed by thedirect-View storage tube.

A further object of the invention is to provide a system of erasure foruse with the direct-view tube in which old stored and displayed data iserased just prior to being replaced with new data.

A further object of the invention is to erase data stored in a tube ofthe above type in a non-synchronous manner so that time-sharing ofwriting and erasing is not required.

A still further object of the invention is to provide an improved signalstorage and display system in which data may be stored for a relativelylong periodof time.

, According to the present invention, improved l'methods and means areprovided for operating the direct-view storage tube. The techniqueemployed herein does not require the special `target assembly describedin application Serial No. 306,706 nor does it require the tin-1esharingarrangement described in application'Serial No. 358,361. y

In the present case pulses are generated non-synchronously with respectto deflections of the tube'writing beam, and are applied to the tube -sothat eitherdata erasure or longer signal storage time is provided. Withthev amplitude of the non-synchronous pulses adjusted below apredetermined level, each applied pulse causes a fractional portion ofthe overall stored charged pattern to beerased. By suitably controllingthe pulse duration and/or amplitude either signal integration orcyclical erasure of the stored data is attainable. With the amplitude ofythese pulses adjusted to be greater than the above-mentionedpredetermined level erasure is not afforded but the storage time of thestored data is increased considerably. l Y

The invention will be described in detail with reference -to theaccompanying drawing in which:

Storage tube structure The drawing shows a direct-view type storage tubeconsisting of an evacuated envelopelltl having two neck sections 12 and14, respectively. Within the envelope neck 12 is an electron gun 16,hereinafter referred to as the viewing gun. Within neck 14 is asecond orwriting electron gun 18 for providing a'modulated beam of electronswhich is accelerated into the envelope portion 10.

Mounted at the large end of the envelope portion l0 is anassemly 20including a glass support sheet 2.?. having a thin Yconductive lm 24disposed on one surface thereof and facing the electron guns. The film24 may be formed,

3 V for example, of a metal or metallic compound such as tin oxide. Ontop of the conductive film 24 is a material 26 such as phosphor whichuoresces under electron bombardment.

In the direction towards the electron guns from the surface of theuorescent material 26 is afstorage target assembly 27. The assembly 27includes ,a 'tine mesh metal screen 28 which is spaced severalmillimeters from the fluorescent material 26. A storage screen 30 isformed, by evaporation or some other convenient means, on the surface ofthe conductive screen 28 and lccmprises a dielectricinsulating materialsuch as a film of silica or magnesium fluoride of the order of severalmicrons in thickness. At a distance of the order of several millimetersfrom the conductive screen 28l in the direction towards the electronguns is a second tine mesh metal screen 32. Screen 32 may be a woven orelectroformed mesh of the order of 100 to 500 mesh per inch. Theconductive screen 28 and the mesh storage screen 30 also may have aineness of the order of 100 to S00 mesh per inch.

Assembly 20 is mounted on a ring 36 of insulating material xed withinthe envelope and adjacent the tube face plate 38. Fixed to the ring 36is an annular metal support ring 40 which supports intermediate its endsthe glass support sheet 22 and across its open end the conductive screen28. Also mounted on the insulating ring 3 6 is a second annular metalsupport ring 42 across the ends of which is mounted the woven orelectroformed metal mesh screen 32. The conductive tin oxide m 24 isinsulated from the support ring 42 by the glass sheet 22 and isconnected by a lead 44 to a source of positive potential outside theenvelope 10. Mesh screen 32 also is connectedto a source of positivepotential via lead 46. The conductive screen 28 during the tubeoperation, is set either to a predetermined bias potential for writingor at a more 'positive potential for erasure or for holding a storedpicture as will be shown hereinafter.

The viewing gun 16comprises a cathode electrode. 48, a control electrode50, a rst accelerating. electrode 52, and a second acceleratingelectrode 54 mountedsuccessively along the axis of the. gun 16 towardthe face plate 38, During the tube operation these electrodes aremaintained at appropriate voltages to form the electron. emission fromthefcathode. 48 into a wide beam or sprayl 56 of electrons for floodinga major portion of the surface of the storage screen. Y The innersurface of the envelope 10 has appliedthereto, a conductive coating 58of colloidal graphitel or tin oxide which coating may be maintained atthe same positiveV potential as the second accelerating electrode` 54. Asecond conductive wall coating 60 extends from a point spaced from. butadjacent coating 58 over the bulb wall enclosing the assemblies and 27.This coatingisata potentialdiferent from that of coating` 58 andthusprovides acollimating electron ,lens to align theelectronsofthespray beam 56 in a direction axially, with respect to thetarget assemblies.

The writing electron gun 18. comprises a cathode electrode 62, a controlelectrode 64; and, successivelyspaced toward the target, afirstaccelerating electrode 66V and ga second accelerating electrode6S.The wall coating 58 extends into the neck 14 of the writing gun andforms a third accelerating electrodefor. forming. the electrons of gun18 into a sharplydeined .andlfocused .beam .70;

The voltages applied to the electrodes of the aboveV tube areillustrative of typical suitable operating voltages but should not beconsidered as. limiting. Forfexample,

the mesh screens 32. may be operatedat between- 200' and 2,000 voltspositive with respect to ground.1 The conductive coating 24 may beoperated within arangeof from 2,000 to 20,000 volts positive relativetoground,

volts relative to. ground.

T ube operation To prepare the storage target for storing a chargepattern on the mesh storage screen 30, it is necessary to establish auniform potential thereover. With the viewing gun turned on, theelectrons of the spray'beam 56 are accelerated with energies of theorder of 1,000 volts through the metal mesh screen 32. The conductivescreen 28, initially biased by a bias source 71 to a potential such aszero volts, is set to a potential suiciently positive (of the order of20 volts positive relative to ground) that the electrons of the spraybeam 56 strike the surface of the storage screen film 30 at velocitiesor energies to initiate secondary emission from all portions of the lrn.In the present example the positive potential of 20 volts which isapplied, as described hereinafter, to the conductive screen 30 is belowthe first crossover point on the secondary ratio curve of the silica (ormagnesium fluoride) film. The first crossover point for a silica storagefilm (see Figure 2) is of the order of 75 to 150 volts while the firstcrossover point for a magnesium fluoride film is approximately 30 to 60volts. Thus secondary emission is initiated having a ratio less thanunity and the storage screen 32 assumes a uniform potential, in thisinstance viewing gun cathode potential. The entire surface of thestorage screen may be brought to a uniform potential as described abovein a fraction of a second.

The potential of the conductive screen 2S is then adjusted toapproximately zero volts (ground potential). Because of the thinness ofthe Storage screen 30, screen 30. is closely' coupled capacitively tothe screen 28, hence the relative potential dilference therebetween ismaintained; i. e., as the potential of screen 28 is changed from a- 20volts positive relative to ground potential, the potential of screen 30changes by a corresponding amount from viewing gun cathode potential(ground potential) to approximately minus 20volts relative to ground.The electrons` of the Spray beam 56 are accelerated through the meshscreen 32 and enter a retarding field adjacent the' screen 30, theretarding field turning the electrons back to the metal screen 32 whichserves as a collector therefor. The 8,000 volt potential applied to thetin oxide lm 24 creates a field which tends to extend through theinterstices of the storage screen 30 to draw electrons through thescreen to bombard the uorescent layer 26. The voltage to which thestorage screen 30 is set (minus 20 volts), however, just prevents anyelectrons from passing therethrough.

The Writing gun 18 is then turned on and produces a sharply defined andfocused beam which may be deflected to scan over the surface of thestorage insulator 30. The `deflection may be accomplished, for example,by supplying vertical and horizontal pairs of deflection plates 72 and74, respectively,` with suitable deflection signals from deflectionsignals from deiiection generators 76and 78, respectively. While thewriting beam 70 is being deflected in the desired pattern, the beam 70is modulated by video signals applied to the writing gun control grid 64from an input circuit 80. The writing beam impinges on the mesh storagescreen 30 at a voltage of approximately 3,000 volts which is between thefirstandsecond cross-over'points on the secondary emission ratio curvethereof.

In this manner the writing beam initiates secondary emission from thesurface of the storage screen such that more electrons leave the surfacethan impinge thereon. In those areas where the beam 70 strikes, thestorage screen surface Iis driven positively from its potential of minus2,0 volts toward-viewing gun cathode potential or ground, ProvidedV theratio of the spray beam average current density to. theaverage currentdensity ofthe writing beam-over a giventime intervall is un-ity orgreater, no point on the insulator surface will stay positively chargedwith respect to ground since electrons from the spray beam 56 landcontinuously at that point and drive it back asserts toA groundpotential, or slightly` negativev with respect to ground. In the areasVwhere the storage screen 3Q. has been driven positively (fromminus20.volts,)f, the. positive ield of the uorescent layer 26 now penetratesto draw the low energy electrons of the spray beam 56 through theinterstices of screens 30- and 2.8 to striloeV the fluorescent screen26. and cause luminescence. 'I-his luminescence 'appears only onareasvof 'the iluorescent screen 26, corresponding to areas of 4thelstorage linsulator driven positively by secondary emission and hence.corresponding to the image pattern. of the writing beam.

This type of writing provides a. visual display in which storedinformation `appears as, white 'on a .dark background. Once a signal hasbeen stored and displayed, theoretically it. should remain .stored anddisplayed indefinitely since thenmodeof tube operation described a'boveis such that the low velocity spray beam 5'6 normally does notv come incontact with the. charged areas of the storage screen 30 and thereforedoes not disturb theA established charge pattern. Actually, however, thecharges established lthereon gradually are. dissipated rby spurious ionsproduced'within the'tu-be.

Erasingr `A synchronizer 82, a pulse generator, produces pulses at apredetermined pulse repetition rate which simultaneously are coupled toa horizontal deflection wave generator 78 and to a pulsevdividercircuit'84. The, divider circuit produces "an output pulse inresponse to a prede- 'termined number of input pulses, Assuming that theinstant method of erasing is to be utilized in connecion with a typicalB-sc-an ra-dar system, and that in the radar system the pulse repetitionrate is 1000 pulses per second .and six seconds is required for a 360azimuth search, the divider circuit 84 produces one output pulse inresponse to each 6,000 input pulses. Each output pulse derived from thedivider 84 is applied to a vertical deflection wave generator 76. Thehorizontal and vertical dellection generators 78 and 7'6, respectively,produce sawtooth deection signal-s which are applied .to the pairs ofdeflection y' plates 72 and 74 of the storage tube to deflect thewriting beam to rectilinearly scan the storage screen 30.

-During the horizontal deflection intervals video signals are applied tothe writing gun control electrode 64 via input circuit 80 Iand modulatethe intensity of the writing 'beam 70 to establish a charge pattern onthe storage screen 30 and a corresponding visual display on theuorescent layer 26.

Entirely independently of lthe generation of the writing deilectionsignals, a free-running multivibrator 86 produces pulses at someselectable repetition rate. A multivibrator which is particularlysuitable for use inthe present erasing system isa free runningpositive-bias multivibrator of the type illustrated at page 269 ofReference Data for Radio Engineers (third edition) publish-ed by theFederal Telephone and Radio Corporation. The multivibrator pulses areamplied in a pulse amplifier 88 having a gain control 90. The amplifieroutput is developed l'across a load impedance 92, each pulse developedthereacross -driving the conductive screen 28 of the storage tubeapproximately 20 volts positive with respect to ground potential.

The erase process is controlled so that each pulse applied to the screen28 causes a 'fractional'portion of the overall stored electrical chargepattern to ybe erased. For example, if Ithe multi-vibrator 8-6-generates 800 pulses per 360 radar search interval, the duration ofeach pulse is Iadjusted 'by means of a pulse duration or Width control94 so .that a given pulse 'causes the overall era-sure of aneight-hundredth of the stored charge pattern. If 1000 pulses are 'to begenerated during this interval the pulse repetition frequency control`96 and the pulse duration con-trol 94 are adjusted so that the desirednumber of pulses are produced and only one one-'thousandth of the chargepattern is erased. T-hus either Ior both the pulse repetition rate` andthe pulse duration, may-bevaried `for erasure yasi-'clesited by suitablyVarying.v circuit constantsin y The circuitry described above may beuseds lt-o achieve long Itime storage of electrical dat-a ratherthanincremental erasure as heretofore shown. According tov-this mode ofoperation the ga-in control is set to control the gain yof the pulse'amplifier 88- so: that lthe pulses` applied to the conductive screen28- .have amplitudes of the order of 60 volts for a magnesium fluorideinsulator andI amplitudes yof the order of volts 'for asilica insulator,in eachcase, just-.abovethei'irstcrossover-point. v Y

' Under su-ch conditions, f or the durationsofthose pulses, portions ofl.the storage-insulator 30 ywhich are carried abovefirst crossoverpotential are lcharged in a positive direction and` :portions of theinsulator 'belowthe rst crossover point' are charged ina negativedirection, The portionscarriedabove .the irst crossover potentialcorrespond to yhighlight portions of- !t-he display providedl on thelfluorescent material 26 `while the insulator portions lbelow lfirstcrossover correspondto darka-reas ofthe display. A single frame of datastored in the manner described above lmay be retained for a period -oftime approximately 103 Itimes longer `than without pulsing.

`In this mode of operation the pulses produced by the multivibrator 86have durations short enough so that no area Iof the storage insulator 30remains equal to or greater than the rst ycr-ossover voltage in theintervals between pulses. IIf lthe pul-se duration 'is too great,electrons from .the viewing beam 56 drive these storage areas to lthepotential of the collector screen 32. Thenthe insulator 30 either maybreak down `or the size of stored charge may increase or ydiminishthereby effectively creeping across the insulator.

What is claimed is:

1. A signal storage system including, an electrical storage tube havingan electron permeable charge storage member, means spaced from one sideof said charge storage member for providing a stream ofv electrons forilooding a major portion of the surface of saidmember, a fluorescentviewing screen spaced from the opposite side of said charge storagemember, means forv providing a sharply defined and focused beam ofelectrons, means for deflecting said sharply defined and focusedelectron` beam across said charge storage member, connection means for asource of signals for modulating said beam during said deflection towrite an electrical charge patfor generating time-spaced pulses at apredetermined pulse repetition rate, and means coupling said pulsegenerating means to said storage tube to pulse said charge storagemember with respect to said Hood beam generating means While saidfocused electron beam is` dellected across said charge storage member.

2. Apparatus as claimed in claim 1 including means for adjusting thepulse duration of said pulses.

3. Apparatus as claimed in claim 1 including means for adjusting thepulse repetition rate of said pulses.

4. Apparatus as claimed in claim l including means for adjusting boththe pulse duration and the pulse repetition rate of said pulses.

5. Apparatus as claimed in claim 1 including means for adjusting theamplitude level of said pulses.

6. A signal storage tube system comprising, an electrical storage tubehaving an electron permeable charge storage member, means spaced fromone side of said charge storage member for providing a stream ofelectrons for ooding a major portion of the surface of said member, afluorescent viewing screen spaced from the opposite side of said chargestorage member, means for providing a sharply defined and focused beamof electrons, means for deecting said sharply defined and focusedelectron beam across said storage member, connection means for a sourceof signals for modulating said beam during said deiiection to write anelectrical charge pattern on said member, the charge pattern written onsaid member modulating the iiow of said stream of electrons so thatelectrons passing through said electron permeable member impinge on saidviewing screen and produce a visual display corresponding to said chargepattern, a free-running multivibrator for repetitively generating pulsesignals, and an amplifier coupled to the output of said multivibratorand to said charge storage member for pulsing said member with ampliedmultivibrator signals While said focused electron beam is deflectedacross said charge storage member.

7. Apparatus as claimed in claim 6 including a gain control circuit foradjusting the gain of said amplifier.

8. A signal storage tube system comprising, an electrical storage tubehaving an electron permeable charge storage member, means spaced fromone side of said CII charge storage member for providing a stream ofelectrons for flooding a major portion of the surface of said member, aiiuorescent viewing screen spaced from the opposite side of said chargestorage member, means for providing a sharply delined and focused beamof electrons, means for deiiecting said sharply defined and focusedelectron beam across said storage member, connection means for a sourceof signals for modulating said beam during said deflection to Write anelectrical charge pattern on said member, the charge pattern Written onsaid member modulating the ow of said stream of electrons so thatelectrons passing through said electron permeable member impinge on saidviewing screen and produce a visual display corresponding to said chargepattern, and means coupled to said charge storage member forrepetitively generating pulses at 4a predetermined pulse repetition ratefor periodically pulsing said storage member while said focused electronbeam is deflected across said charge storage member.

References Cited in the le of this patent UNITED STATES PATENTS2,513,743 Rajchman July 4, 1950 2,532,339 Schlesinger Dec. 5, 19502,548,789 Hergenrother Apr. 10, 1951 2,612,634 Mesner Sept. 30, 19522,706,246 Klemperer Apr. l2, 1955

